Electro-acoustic transducers

ABSTRACT

An electro-acoustic transducer for use in telephones having a Ushaped magnetic conducting yoke with an electromagnetic coil around one leg of the yoke. A substantially flat armature connected at one end to the diaphragm by means of a drive rod is pivotably mounted on a permanent magnet located intermediate the legs of the yoke. A strip of non-magnetic compliant material interposed in the gap between the armature and the opposing yoke ends defines the thickness of the gap, prevents magnetic leakage therethrough and prevents the ingress of foreign particles into the polar gaps.

United States Patent Dymoke-Bradshaw Nov. 11, 1975 [54] ELECTRO.ACOUSTIC TRANSDUCERS 3.334.195 8/1967 Ashworth 179/1 15 R [75] Inventor: Leslie E. B. Dymoke-Bradshaw, FOREIGN PATENTS OR APPLICATIONS Edgware- England 1.061.137 3/1967 United Kingdom .1 179/115 A [73] Assignee: International Standard Electric C i New York, Primary E.\'aminerl(athleen H. Claffy Assistant E.\'uminerGeorge G. Stellar [22] F'led: 1974 Attorney, Agent. 01' Fi1'mJohn T. OHalloran; [21] Appl, N 445,708 Menotti J. Lombardi, Jr.; Richard A. Menelly [30] Foreign Application Priority Data [57] ABSTRACT Mar W73 United Kingdom 14545/73 An electro-acoustic transducer for use in telephones having a U-shaped magnetic conducting yoke with an [52] us CL 179/115 l79/l8O electromagnetic coil around one leg of the yoke. A [51] Int. c1.-..........II.II...IIIII H0 4R 11/00 Substantially flat mature Connected at the [58] Field of Search 179/114 R, 115 R, 114 A, dlaphmgm by means f a dnve rod pwouibly 179 ll 15 A 180 mounted on a permanent magnet located intermediate the legs of the yoke. A strip of nonmagnetic compli- [56] References Cited ant material interposed in the gap between the armature and the opposing yoke ends defines the thickness UNITED STATES PATENTS of the gap, prevents magnetic leakage therethrough l jf g 36535 4 and prevents the ingress of foreign particles into the lS er I 2.588.327 3/1952 Roberts et al. 179/114 A polar gaps. 3.111.496 1l/l963 Hunter et a1 260/25 H 5 Claims, 5 Drawing Figures US. Patent Nov; 11,1975 3,919,509

'1 ELECTRO -ACOUSTIC TRANSDUCERS" BACKGROUND OF THE INVENTION Rocking armature transducers generally consist of a substantially flat armature that is pivoted to respond relative to alternating magnetic fields incluced'into a magnetic conducting yoke by means of an electromagnetic coil winding. The armature is connected by means of a drive rod to a diaphragm so that when the transducer is used as a speaker, voice currents through the electromagnetic coil cause the armature to vibrate correspondingly to the fluctuations electromagnetically induced by the coil and sends vibrations via the drive rod to the diaphragm. When the trans'ducer'is used as a microphone, vibrations from the diaphragm are then transmitted by means of the drive rod to the armature, which in turn causes voicecur rents to flow in theelectromagnetic coil. Since the armature is usually pivotably mounted, it is susceptible to variationsin themagnetic flux which may exist between the ends of the armature. In order to overcome and control the magnetic variations between the ends of the armature. and, for example, the magnetic conducting yoke,asserr ibly,.torsion arms aregenerally provided in order to insure that equal forces will exist on both ends of the armature; and means are usually provided during manufactureto adjust the torsion arms. The vibrational properties of the armature, sometimes referred to as armature stiffness, can then be controlled by the torsion properties of the torsion arms.

The armatures currently being used; for example, in telephone sets, generally have an air gap existing between the ends of the legs of the yoke and the ends of the armature. It is possible for foreign magnetic material to fall into this gap and to cause magnetic leakage to occur in, for example, one leg of the yoke. The armature is now subjected to unequal magnetic forces which tend to unbalance the armature from its stable position on its pivot. Any foreign material bridging an air gap introduces another stiffness to the system with consequent loss of sensitivity. This is the main hazard.

Since the gap is now controlled by the thickness of the material and since the gap is completely filled, no foreign material can enter therein. Another advantage that exists with the use of the non-magnetic compliant material to fill the gap is that the vibrational characteristics; that is, the so-called armature stiffness control, can now be controlled by the mechanical properties of this non-magnetic compliant material. Torsion arms requiring mechanical adjustment are no longer necessary since the armature balance is now insured by the presence of the compliant material in the gap.

SUMMARY OF THE INVENTION This invention comprises an electro-acoustic transducer, which includes a yoke ofa magnetically soft material which is generally U-shaped; and this has two legs, a third leg between the legs of the yoke which includes a DC. magnetic flux source, the yoke with said third leg being thus generally E-shaped, an armature of a magnetically soft material across the legs of the E and having each of its ends facing the end of one of the legs of the yoke, speech coil means on the yoke, pads of non-magnetic and compliant material between the end of each leg of the yoke and its end of the armature so that the pads define the dimensions of the gaps and the armature stiffness, an extension on one end of the armounting.

mature which carries a connecting rod, and a diaph'rag'm connected by the rod to the armature extension so that rocking movement of the armature drives the diaphragm or vice versa.

ERIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a side view of the transducer of this in- FIG. 4 is a top view of the frame used for mounting the completed armature of this invention.

FIG. 5 is a side view of the armature of this invention showing the connection between the diaphragm and the armature.

DESCRIPTIONOF'PREFERREI) EMBODIMENT Referring to FIGS. 1 3, these show the drive unit without its coil, which is wound on the leg 1 of the yoke. The magnet 2 is mounted, as usual, onthe base of the U-shaped yoke so that the magnet plus yoke are together E-shaped. The armature is pivoted on the magnet 2, by a ridge 4 running across its lower face. At its right-hand end the armature 3 has an extension 5 to which the drive rod 9 for the diaphragm is attached 30 see FIG. 5).

The single coil 15 which embraces the pole-piece leg remote from the drive rod is held in place by sticking it to the leg, or by throwing up two barbs on the polepiece leg and forcing the spool over them. On this latter case the spool and coil are held in place by a fishhook action. Another method of retention is to redesign the spool check so that an integrally-moulded barb or barbs hooks under the frame. Again, one or more spigots can be thrown up on the frame which, after it has been headed over in mushroom fashion provides latching means with a spool check.

The stiffness control which has hitherto been provided by the torsion arms is provided by strips 6, 6 of a compliant non-magnetic material stuck into the gaps between the pole faces on the outer legs of the E and the armature 3. This material, which in one example is a modified form of polyisobutylene, is therefore the controlling stiffness. Since, as can be seen from the drawings, the pole gaps are filled, ingress of foreign material into the gaps is not possible; and the gap balance is controlled by the thickness of the material. Torsion arms are no longer necessary, and the fixing legs for the yoke which have sometimes been necessary in previously known devices are no longer needed.

The unit shown in FIGS. 1 3, plus a speech coil on its limb l, is stuck to a frame shown in plan in FIG. 4. This frame has a locating means at 7 which receives a recessed strap 8 (FIG. 5) into which the yoke fits.

As can be seen from FIG. 5, the extension 5 is coupled by a drive rod 9 to the diaphragm 10.

Another method of assembly is to extend the side portion of the yoke 11, FIG. 2, to form lugs, which are drilled. The holes in these lugs are aligned with holes in the frame and the drive unit and frame secured together with rivets or self-tapping screws.

The construction described is such that fewer magnetic leakage paths exist than in known rocking armature transducers, which enables a smaller magnet of the same magnetic parameter. or a similar-sized magnet with inferior parameters, to be used. This, of course, reduces cost.

Although the drawing shows the preferred used fulcra, either one ridge across the armature or two or more aligned pips on it, the mechanism is operable without these, since one padded air gap can act as a pivot on one A.C. halfcycle and vice versa,

Another useful feature is that, depending on the physical properties of the pads, a degree of mechanical damping should occur, which damps out the electromechanical resonance of the armature system.

it is to be understood that the foregoing description of specific examples of this invention is made by way of example only and is not to be considered as a limitation on its scope.

I claim:

1. An improved rocking armature transducer of the type having a U-shaped magnetic conducting yoke, a permanent magnet, an armature, an electromagnetic coil, and a diaphragm wherein the improvement comprises:

a magnet located intermediate said U-shaped magnetic conducting yoke;

an armature pivotably located upon said magnet by means of at least one protrusion on said armature and having each end of said armature opposite each end of said yoke;

an electromagnetic coi] located on one leg of said yoke;

a diaphragm connected to an extension on said armature by means ofa drive rod for communicating vibrations from said armature to said diaphragm; and at least one strip of compliant non-magnetic material interposed between the legs of said yoke and the ends of said armature for preventing said armature from contacting said yokc.

2. An improved rocking armature transducer of the type having a U-shaped magnetic conducting member, a magnet, a diaphragm, an armature, and an electromagnetic coil surrounding one leg of said U-shaped magnetic conducting member wherein the improvement comprises:

said armature pivotably mounted on said magnet having first and second ends proximate first and second ends of said U-shaped magnetic conductng member so that the armature vibrates in response to current flow through said electromagnetic coil; and

first and second strips of compliant nonmagnetic material interposed between said first and second ends of said U-shaped member and said first and second ends of said armature for preventing said armature ends from contacting the ends of said magnetic member.

3. The transducer of claim 2 further including a drive rod interconnected between said first end of said armature and said diaphragm for transmitting vibrations from said armature to said diaphragm.

4. The transducer of claim 2 wherein the compliant non-magnetic material comprises polyisobutylene.

5. The transducer of claim 2 wherein said armature includes an extension thereon for providing a pivot point for mounting on said magnet. 

1. An improved rocking armature transducer of the type having a U-shaped magnetic conducting yoke, a permanent magnet, an armature, an electromagnetic coil, and a diaphragm wherein the improvement comprises: a magnet located intermediate said U-shaped magnetic conducting yoke; an armature pivotably located upon said magnet by means of at least one protrusion on said armature and having each end of said armature opposite each end of said yoke; an electromagnetic coil located on one leg of said yoke; a diaphragm connected to an extension on said armature by means of a drive rod for communicating vibrations from said armature to said diaphragm; and at least one strip of compliant non-magnetic material interposed between the legs of said yoke and the ends of said armature for preventing said armature from contacting said yoke.
 2. An improved rocking armature transducer of the type having a U-shaped magnetic conducting member, a magnet, a diaphragm, an armature, and an electromagnetic coil surrounding one leg of said U-shaped magnetic conducting member wherein the improvement comprises: said armature pivotably mounted on said magnet having first and second ends proximate first and second ends of said U-shaped magnetic conductng member so that the armature vibrates in response to current flow through said electromagnetic coil; and first and second strips of compliant non-magnetic material interposed between said first and second ends of said U-shaped member and said first and second ends of said armature for preventing said armature ends from contacting the ends of said magnetic member.
 3. The transducer of claim 2 further including a drive rod interconnected between said first end of said armature and said diaphragm for transmitting vibrations from said armature to said diaphragm.
 4. The transducer of claim 2 wherein the compliant non-magnetic material comprises polyisobutylene.
 5. The transducer of claim 2 wherein said armature includes an extension thereon for providing a pivot point for mounting on said magnet. 